Boiler displays error 29, often associated with condensate drainage problems in condensing models.

Safety: Isolate power before working on the condensate system. Condensate is mildly acidic; wear gloves and eye protection.

• Check external pipe: Inspect the external condensate pipe for freezing or blockage. Thaw gently with warm (not boiling) water and lag the pipe to prevent re-freezing.
• Clean condensate trap: Remove the condensate trap/siphon under the boiler. Empty and rinse it thoroughly to remove sludge and debris. Ensure the internal baffle is intact.
• Verify pipe fall: Ensure the condensate pipe runs with a continuous fall to the drain and has no upward loops that can trap water.
• Prime the siphon: Refit the trap and fill it with clean water to ensure a proper water seal before restarting the boiler.
• Test operation: Restore power and run the boiler. Confirm that condensate flows freely and error 29 does not reappear.